NASA successfully deflects asteroid in planetary defence test

After 10 months flying in space, NASA’s Double Asteroid Redirection Test (DART) spacecraft has successfully impacted its asteroid target, in the agency’s first attempt to intentionally collide with an asteroid in space in order to deflect it — a technique known as kinetic impact. Mission control at the Johns Hopkins University Applied Physics Laboratory (APL) in Maryland, USA, announced the successful impact today at 9.14 am AEST (7.14 pm on Monday EDT).

As part of NASA’s overall planetary defence strategy, DART targeted the asteroid moonlet Dimorphos, a small body just 160 m in diameter that orbits a larger, 780 m asteroid called Didymos. Neither asteroid poses a threat to Earth, but DART’s impact with the asteroid demonstrates a viable mitigation technique for protecting the planet from an Earth-bound asteroid or comet, if one were discovered.

The spacecraft’s sole instrument, the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), together with a sophisticated guidance, navigation and control system that works in tandem with Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav) algorithms, enabled DART to identify and distinguish between the two asteroids, targeting the smaller body. These systems guided the 570 kg, box-shaped spacecraft through the final 90,000 km of space into Dimorphos, intentionally crashing into it at roughly 22,530 km/h to slightly slow the asteroid’s orbital speed.

“Planetary Defense is a globally unifying effort that affects everyone living on Earth,” said Thomas Zurbuchen, Associate Administrator for the Science Mission Directorate at NASA headquarters. “Now we know we can aim a spacecraft with the precision needed to impact even a small body in space. Just a small change in its speed is all we need to make a significant difference in the path an asteroid travels.”

A global team is now using dozens of telescopes stationed around the world and in space, as well as images produced by DART and its CubeSat companion Light Italian CubeSat for Imaging of Asteroids (LICIACube), to observe the asteroid system. Over the coming weeks, they will characterise the ejecta produced and precisely measure Dimorphos’s orbital change to determine how effectively DART deflected the asteroid; the researchers expect the impact to shorten Dimorphos’s orbit by about 1%, or roughly 10 minutes. The results will help validate and improve scientific computer models critical to predicting the effectiveness of this technique as a reliable method for asteroid deflection.

The European Space Agency’s Hera project will also conduct detailed surveys of both Dimorphos and Didymos roughly four years from now, with a particular focus on the crater left by DART’s collision and a precise measurement of Dimorphos’s mass.

“DART’s success provides a significant addition to the essential toolbox we must have to protect Earth from a devastating impact by an asteroid,” said Lindley Johnson, NASA’s Planetary Defense Officer. “This demonstrates we are no longer powerless to prevent this type of natural disaster. Coupled with enhanced capabilities to accelerate finding the remaining hazardous asteroid population by our next Planetary Defense mission, the Near-Earth Object (NEO) Surveyor, a DART successor could provide what we need to save the day.”

Also commenting on the milestone was Professor Alan Duffy, Director of the Space Technology and Industry Institute at Swinburne University of Technology and Lead Scientist at The Royal Institution of Australia. He said the achievement shows that humanity “doesn’t have to go the way of the dinosaurs”.

“The technical ability to hit a target just 160 metres wide after a distance of 11 million kilometres is akin to striking a dartboard from across the Earth, and to do that at 25,000 km/h is simply beyond amazing as the target grows in view from something no larger than your thumb at arm’s length to impact within two seconds,” Duffy said.

“Preventing an object the size of Dimorphos from hitting the Earth is key as while they’re not common they are by no means rare, expected to hit every 20,000 years or so. Thanks to their great speed, even this small an object would impact with an energy release equivalent to thousands of nuclear bombs, leaving a crater 3 km across and annihilating everything in a blast wave stretching hundreds of kilometres. We want to find and prevent these asteroids, and now thanks to NASA DART we know we can.”

Illustration depicts NASA’s Double Asteroid Redirection Test (DART) spacecraft prior to impact at the Didymos binary asteroid system. Image credit: NASA/Johns Hopkins APL/Steve Gribben.

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